The present invention relates to a component configured for being subjected to a high thermal load during operation, comprising a wall structure with cooling channels adapted for handling a coolant flow, wherein at least one first cooling channel is adapted to convey the coolant from a first portion of the component to a second portion of the component.
The component will in the following be described for being used as a rocket engine component. This application should be regarded as preferred. However, also other applications are possible, such as for a jet motor or gas turbine.
The component is in operation actively cooled by a coolant flowing in said cooling channels. The coolant may further be used for combustion after having served as a coolant. The present invention is specifically designed for a regeneratively cooled liquid fuel rocket engine.
The rocket engine component in question forms a part of a combustion chamber and/or a nozzle for expansion of the combustion gases. The combustion chamber and the nozzle are together commonly referred to as a thrust chamber.
During operation, a rocket engine component forming a combustion chamber and/or an outlet nozzle is subjected to very high stresses. A nozzle is for example subjected to a very high temperature on its inside (in the magnitude of 800° K) and a very low temperature on its outside (in the magnitude of 50° K). As a result of this high thermal load, stringent requirements are placed upon the choice of material, design and manufacture of the nozzle. At least there is a need for an effective cooling of the nozzle.
The wall structure forming the nozzle has a tubular shape with a varying diameter along a centre axis. More specifically, the outlet nozzle wall structure has a conical or parabolic shape. The outlet nozzle normally has a diameter ratio from the aft or large outlet end to the forward or small inlet end in the interval from 2:1 to 4:1.
The outlet nozzle wall structure comprises cooling channels extending between an upstream end and a downstream end of the nozzle. According to one previously known design, the outlet nozzle wall structure comprises an inner wall, to which hot gas is admitted during engine operation and an outer wall, which is colder than the inner wall during engine operation. A plurality of elongated webs is adapted to connect the inner wall to the outer wall dividing the space between the walls into a plurality of cooling channels.
During engine operation, any cooling medium may be used to flow through the cooling channels. Regarding a rocket engine, the rocket engine fuel is normally used as a cooling medium in the outlet nozzle. The rocket engine may be driven with hydrogen or a hydrocarbon, i.e. kerosene, as a fuel. Thus, the fuel is introduced in a cold state into the wall structure, delivered through the cooling channels while absorbing heat via the inner wall and is subsequently used to generate the thrust. Heat is transferred from the hot gases to the inner wall, further on to the fuel, from the fuel to the outer wall, and, finally, from the outer wall to any medium surrounding it. Heat is also transported away by the coolant as the coolant temperature increases by the cooling. The hot gases may comprise a flame generated by combustion of gases and/or fuel.
The basic problem is to construct cooled nozzle walls that are capable of containing the hot gas and accelerate the gas and to be able to do so in a reliable way for a required number of engines service cycles. The coolant needs to be distributed in a precise way to use the available coolant in an efficient way and to avoid local deficiencies in cooling performance.
It is desirable to arrange coolant ducts to and from the nozzle in such a way that the size of manifolds and length of the ducts are minimized. Furthermore, it is desirable to place the manifolds in areas of the nozzle where it is protected from high level of vibration and external flow and heat loads. The previously known designs do not fully meet these requirements.
A first previously known design is a so-called single pass flow arrangement. The coolant inlet is at the top and the outlet is at the bottom of the nozzle, or vice versa. Thus, the direction of the flow could be up-path or down-path. The coolant duct connected to the manifold at the bottom of the nozzle will in this case be very long.
A second previously known design is a so-called double pass flow arrangement. The full double path coolant layout has the inlet and outlet at the same axial location, at the top of the nozzle. The manifolds are placed at the desired position and the ducts are the shortest possible. However it is difficult to find a practical arrangement between manifolds and the entrance to and exits from the wall structure.
A third previously known design is a so-called balanced double pass flow arrangement. The inlet is at the top of the nozzle. The flow is directed in the same direction in two adjacent cooling channels in a first part of the nozzle. One of the channels leads directly to an outlet, which is placed between the top and the bottom of the nozzle. The other channel extends to the bottom of the nozzle. The coolant in the other channel is led to the bottom of the nozzle and thereafter upwards in the first channel to the same outlet. The axial position of the inlet and outlet are separated and hence the access to the wall is good. The outlet manifold needs to be placed a significant distance from the inlet manifold to achieve a close to equal distribution between the channels. Therefore the size of the outlet manifold and its duct is not of minimum size. Unbalance in the flow means inefficient cooling and reduced life. The mass flow distribution in the two flow paths is decisive of the pressure drop. The distribution could vary since small differences in inlets, the channels, turning manifolds and outlets could affect the flow.
It is desirable to achieve a component, which creates conditions for an improved heat exchange and a sufficient design with regard to external coolant ducts and manifolds. The component should be especially suitable for a rocket engine. Especially, the invention aims at a component that creates conditions for arranging the coolant ducts to and from the component in such a way that the size of manifolds and length of the ducts are minimized. Furthermore, the invention aims at a component that creates conditions for placing the manifolds in areas of the component where it is protected from high level of vibration and external flow and heat loads.
Thus, an aspect of the invention is characterized in that at least one second cooling channel in the second portion is closed so that the coolant is at least substantially prevented from entering the closed second cooling channel from a cooling channel in the first portion.
The wording “at least substantially prevented from entering” means that either all coolant flow is prevented from entering or only a very small part, for example maximum 3%, of the coolant flow from the first portion may enter the second cooling channels.
The first portion of the component may thereby be configured for a very high heat load in that it will have optimum cooling efficiency. In the case of a rocket engine nozzle, the heat load is at a maximum in an upper part, wherein the invention creates conditions for an optimum cooling efficiency with no variation in angular direction between individual cooling channels.
Further, the cooling performance is identical between cooling channels for the uppermost part of the nozzle where the heat load is at maximum. This is especially important in case of less efficient cooling medias such as methane.
According to a preferred embodiment of the invention, the second portion of the component comprises twice the number of cooling channels in the first portion. Further, every other cooling channel in the second portion is closed so that the coolant is prevented from entering the closed cooling channels from the cooling channels in the first portion. These features create conditions for sufficient cooling of a component with an increasing width, such as in a component with a circular cross section where a cross section diameter varies in an axial direction of the component.
The component comprises at least one inlet in the first portion for entrance of the coolant and at least one outlet in the second portion for exiting the coolant. Preferably, the outlet is positioned in the closed cooling channel in the second portion and in the vicinity of the closure. In this way, the outlet manifold may be placed very close to the inlet manifold, the main concern being the access to the wall structure to arrange inlet and outlet ports.
Further, a robust flow balance is achieved due to the controlled one-way flow from the inlet to the outlet in relation to the so-called balanced double pass flow arrangement (see above). In other words, any disturbance is less likely to cause problems in the flow balance. Especially, the cooling is less sensitive to differences in pressure drops in the cooling channels. So-called hot spots are non-desirable in the wall structure during engine operation. Hot spots may arise due to a geometrical variation or a thermal variation in the cooling channels. The ability of cooling to handle hot spots is improved with the inventive controlled flow solution since the flow is one-way and pressure balancing is not an issue.
According to a preferred embodiment of the invention, at least one of said cooling channels in the first portion is split into two channels in the second portion, that one of the two split channels is closed and the other channel is open so that the coolant may enter the open cooling channel from the cooling channel in the first portion. Thus, the cooling channel is split up in two channels. However the flow is not split up. One of the split channels is closed. The other split channel is open, preferably to a bottom of the component.
According to an alternative to the last-mentioned embodiment, a width of a cooling channel in the first portion, which coincides with an open cooling channel in the second portion, is substantially the same as a width of the open cooling channel in the second portion in a transition region between the first and second portion.
Preferably an end of a transition wall separating two adjacent channels in the first portion covers the second cooling channel in the second portion and thereby forms the closure. Further, the division wall preferably has an increasing thickness in the cooling channel direction. Such a design creates conditions for a facilitated manufacturing process in that the first and second portions can be manufactured in separate pieces and joined in a later step.
Further preferred embodiments and advantages will be apparent from the following description and drawings.